As massive consumption of fossil fuels has been continuing, global warming, air pollution in urban areas, and the like caused by carbon dioxide, have become serious. In this situation, attention is focused on hydrogen as an energy source that will take a measure role in the next generation to take the place of fossil fuels. Hydrogen can be electrolytically produced, utilizing renewable energy represented by photovoltaic battery, wind power, or the like for example. Further, only water is produced by burning hydrogen. Accordingly, hydrogen is a clean energy source with little emission of environmental pollutant through producing and using.
As a method of producing hydrogen, steam-reforming of fossil is industrially and widely applied. Further, there are known other various producing methods including reaction using by-product hydrogen in producing iron or soda, thermal decomposition, photocatalyst, microorganisms, or electrolysis of water. Particularly, it is possible to use electrical powers from various kinds of supply sources as a power necessary for electrolysis of water. Accordingly, the importance of methods of producing hydrogen by electrolysis of water is emphasized as methods of producing an energy source without depending on a certain area.
However, in using hydrogen as an energy source (namely fuel), transportation, storage, a supply system or the like can be significant problems. Concretely, as hydrogen is in a gas state at an ordinary temperature and pressure, storage and transportation of hydrogen are more difficult problems than those of liquid and solid. Further, hydrogen is a flammable material and possibly reacts explosively when air and hydrogen are mixed at a certain mixture ratio.
As a technology to solve these problems, for example, Patent Document 1 discloses a fuel cell electrical power generator system wherein hydrocarbon fuel is subjected to desulfurization by a desulfurization device; water vapor is thereafter added to the hydrocarbon fuel; the hydrocarbon fuel is supplied to a steam reforming unit; hydrogen is generated here; this hydrogen is supplied to a fuel cell; and the hydrogen is subjected to reaction with oxygen so that electrical energy is taken out.
Further, recently, as hydrogen storage methods excellent in safeness, transportability, and storage capacity, attention is focused on organic hydride systems using hydrocarbon, for example, cyclohexane, decalin, etc. Being liquid at an ordinary temperature and pressure, these hydrocarbons are easier to store and transport than a case of gas. For example, benzene and cyclohexane are cyclic hydrocarbons with the same carbon number, wherein benzene is an unsaturated hydrocarbon with double bond, while cyclohexane is a saturated hydrocarbon without double bond. That is, cyclohexane, which is a saturated hydrocarbon, is obtained by hydrogenating benzene, which is an unsaturated hydrocarbon. Also, benzene is obtained by desorbing hydrogen from cyclohexane. For example, Patent Document 2 discloses a system capable of storing and supplying hydrogen by utilizing hydrogenation reaction and hydrogen desorption reaction by the use of benzene and cyclohexane in such a manner.
However, in order to build an organic hydride system using renewable energy, there are cases that it is necessary to consider the electric energy (namely electrical power generation amount) by the renewable energy into account. In other words, the electrical power generation capacity by renewable energy ordinarily varies with weather conditions. For example, an electrical power generation capacity varies with the strength/weakness of wind in a case of wind power generation using wind power as a renewable energy, and varies with the strength/weakness of sunshine and hours of sunshine in a case of photovoltaic power generation using solar light.
In order to respond to such variation in the electric energy, for example, Patent Document 3 discloses a wind-power-generation hydrogen production device that includes a wind power generator device for supplying electrical power to a load and an electrolytic hydrogen production device that is supplied with electrical power from the wind power generator device, wherein, with a preset electrical power to be supplied to the load as a target value, the difference between the electrical power output from the wind power generator device and the target value is supplied to the electrolytic hydrogen production device.
Further, Patent Document 4 discloses a hydrogen using system provided with a controller that controls operation of a water electrolysis device, corresponding to the cost of commercial electrical power, the hydrogen consumption amount of a hydrogen using device, and the hydrogen storage amount by hydrogen storing means.